my $sv_name = $specialsv_name[$sv_index];
Certain SV types are considered 'special'. They're represented by
-B::SPECIAL and are refered to by a number from the specialsv_list.
+B::SPECIAL and are referred to by a number from the specialsv_list.
This array maps that number back to the name of the SV (like 'Nullsv'
or '&PL_sv_undef').